This invention pertains to bidirectional amplifiers, in general, and to a bridge amplifier for an electronic telephone set in particular.
Such amplifiers are needed in so-called telephone circuits, i.e., telephone subscriber's instrument circuits in which the transducers are coupled to the telephone line via amplifiers. Such amplifiers, and indeed the whole instrument circuit, are preferably line-powered. In such case, it is highly desirable for the circuit to be polarity insensitive, since one can never be certain without performing tests which of the two wires is the more positive one. It is also desirable for the circuit of such a telephone to be so designed as to be usable in a wide variety of telephone line conditions.